In recent years, the measurement of blood oxygen saturation, commonly referred to as oximetry, has come into increasingly widespread use during surgical procedures as a means for monitoring and preventing undetected hypoxemia of the surgical patient. Essentially, oximetry measures the amount of oxygenated hemoglobin in the blood of the patient as a percentage of the total hemoglobin in the blood. Various devices, typically referred to as oximeters, are available for performing oximetry measurements.
So-called non-invasive pulse oximeters are configured to attach to a patient's fingertip, ear lobe, or nose and are operable to transmit light of different wavelengths or colors, typically in the red and infrared spectrums, into the body part and to detect the light transmitted therethrough or the light reflected thereby. It is known that the ability of blood hemoglobin to absorb light varies in relation to the level of oxygenation of the hemoglobin. Accordingly, detection of the reflected or transmitted light from a pulse oximeter indicates the amount of the light absorbed from which the blood oxygen saturation can be calculated.
While the non-invasive pulse oximeters of the aforementioned type provide substantial advantages over previous oximetry methods, which required the withdrawal of blood samples from a patient, pulse oximeters are still subject to several disadvantages. First, since existing oximeters are typically attached to peripheral areas of the patient's body, when the patient is in the state of low blood profusion, e.g., when the patient has lost a substantial amount of blood, is cold, or has peripheral vascular disease, or for other reasons has poor blood circulation, difficulty may often be experienced in obtaining a sufficient light transmission or reflectance signal from which to calculate the patient's blood oxygen saturation. This is particularly so in cases of shock or hypothermia or other conditions of lowered or inconsistent circulation. Likewise, the ambient light sources and relative movement of the patient and the oximeter may also interfere with the accuracy of the measurements and calculations obtained.
One type of oximetry device employing such non-invasive methods is disclosed in U.S. Pat. No. 4,928,691 which issued on May 29, 1990 to Nicolson et al. This device is a rigid but malleable sensor probe which may be attached to the tongue and has a light source and sensor attached thereto for transmitting light through the tongue tissue to obtain blood oxygen saturation measurements.
As with the device described in the '691 patent, one problem with previous oximetry devices is the fact that the oximetry device is an additional device needed during the surgical or other procedure. The addition of such devices during the surgical procedure increases both the expense and complexity of any surgical procedure. U.S. Pat. No. 5,005,573 to Applicant and issued on Apr. 9, 1991 discloses an endotracheal breathing tube for use in surgical operations which is equipped with a light emitting device adjacent its distal end to reside within the patient's trachea during use and with a compatible photosensitive detector positionable outside the patient's body in contact with the neck to intercept the light transmitted from the light emitting device for performing accurate oximetry measurements and calculations of the patient's blood oxygen saturation.
While the device disclosed in the '573 patent does eliminate the need for a separate oximetry device, it still requires the surgeon or assistant to position the light receiving or detecting device securely on the patient and may still fail to make a reading should the device on the patient's neck be shifted accidentally. It would therefore be beneficial to provide for an oximetry device which is a part of a device already used as surgery, which does not require the attention of medical personnel to accomplish the positioning of the light transmitting or light receiving device, and which yields precise oxygen saturation readings for those patients whose lowered or inconsistent circulation produces inaccurate readings in sensors located at peripheral sites.